1. Field of the Invention
The present invention relates to a surface-coated cutting member in which the bonding of a hard coating to a substrate is enhanced so highly that the hard coating is hardly subjected to separation, thereby exhibiting excellent wear-resistance over a prolonged period of time.
2. Prior Art
There have been extensively used surface-coated cutting members each of which comprises a substrate made of a hard material of tungsten carbide-based cemented carbide, titanium carbo-nitride based cermet or high speed steel, and a hard coating formed on a surface of the substrate and comprising one or more layers each composed of one or more carbide of metal in Groups IVa, Va or VIa of the Periodic Table, nitride of metal in Groups IVa or Va of the Periodic Table, oxide of metal in Group IVa of the Periodic Table, and solid solution of two or more of these compounds.
Each conventional cutting member mentioned above, however, has been found that the bonding of the hard coating to the substrate is not sufficient. Consequently, when the cutting member is used to carry out a heavy-duty cutting operation such as high-speed cutting, high-feed cutting, deep cutting and the like, the hard coating is subjected to separation or wear after a relatively short time to result in a short tool life of the cutting member.
It is therefore an object of the present invention to provide a surface-coated cutting member in which the bonding of a hard coating to a substrate is highly enhanced to provide a high wear-resistance.
According to the present invention, there is provided a surface-coated cutting member comprising a substrate of hard material selected from the group consisting of tungsten carbide-based cemented carbide, titanium carbo-nitride based cermet and high speed steel, a layer of metal vapor-deposited on a surface of the substrate and having an average thickness of 0.1 to 1 .mu.m, the metal being selected from Group IVa of the Periodic Table, and a hard coating vapor-deposited on the metal layer and having an average thickness of 1 to 9 .mu.m, the hard coating consisting of an inner layer of an average thickness of 0.2 to 4 .mu.m vapor-deposited on the metal layer, an intermediate layer of an average thickness of 0.2 to 4 .mu.m vapor-deposited on the inner layer and an outer layer of an average thickness of 0.2 to 3 .mu.m vapor-deposited on the intermediate layer, the inner layer being made of carbide or carbo-nitride of metal selected from Group IVa of the Periodic Table, the intermediate layer being made of carbo-nitride of metal selected from Group IVa of the Periodic Table, the outer layer being made of nitride of metal selected from Group IVa of the Periodic Table.